Active noise control system

A system for attenuating undesirable noise produced by a noise source, wherein the undesirable noise contains multiple sinusoidal noise components each having a different frequency, the system comprising:

• means for deriving a reference input signal having a value that is functionally related to the frequency of each of multiple noise components contained in the undesirable noise;
• a plurality of signal generators each producing a respective signal generator output signal in response to the reference input signal value, and each generator output signal contains at least one sinusoidal signal component varying at a frequency corresponding to that of a respective one of the multiple noise components, wherein signal component varying at frequencies corresponding to those of noise components that are adjacent with respect to frequency are contained in different ones of the generator output signals and at least one of the plurality of generator output signals contains at least two sinusoidal signal components and each generator output signal is derived from a respective predetermined schedule of values based upon the reference input signal value, with the values in the respective predetermined schedule being obtained from a summation containing at least one sinusoidal term having an argument related to an integer multiple of the reference input signal value;
• a plurality of adaptive filters, each adaptive filter operating to filter a respective one of the generator output signals to produce a corresponding filter output signal in accordance with filtering characteristics of the adaptive filter;
• summing means for adding each filter output signal to produce an output canceling signal;
• means for generating noise canceling waves in response to the output canceling signal and for superimposing the canceling waves with the undesirable noise, whereby the undesirable noise is attenuated;
• means for sensing a residual noise level resulting from the superposition of the canceling waves and the undesirable noise and for developing an error signal indicative of the residual noise level;
• and
• means for adaptively adjusting the filtering characteristics of each one of the adaptive filters in accordance with the error signal to reduce the sensed level of residual noise.

A system for attenuating undesirable noise generated by an internal combustion engine, wherein the undesirable noise contains multiple sinusoidal noise components each having a different frequency related to the time rate of change of the angular rotational position of the engine in its operating cycle, the system comprising:

• means for sensing the angular rotational position of the engine in its operating cycle;
• a plurality of signal generators each producing a respective generator output signal in response to the sensed rotational position of the engine in its operating cycle, each generator output signal containing at least one sinusoidal signal component varying at a frequency corresponding to the frequency of a respective one of the multiple noise components, wherein sinusoidal signal components varying at frequencies corresponding to those of noise components that are adjacent with respect their frequencies are produced by different ones of the signal generators and at least one of the plurality of generator output signals contains at least two sinusoidal signal components;
• a plurality of adaptive filters, each adaptive filter operating to filter a respective one of the generator output signals to produce a corresponding filter output signal in accordance with filtering characteristics of the adaptive filter;
• summing means for adding each filter output signal to produce an output canceling signal;
• means for generating noise canceling waves in response to the output canceling signal and for superimposing the canceling waves with the undesirable noise, whereby the undesirable noise is attenuated;
• means for sensing a residual noise level resulting from the superposition of the canceling waves and the undesirable noise and for developing an error signal indicative of the residual noise level;
• and
• means for adaptively adjusting the filtering characteristics of each one of the adaptive filters in accordance with the error signal to reduce the sensed level of residual noise.